The recovery of high purity lead oxide materials (99.99+%) from lead acid battery pastes has been a long standing requirement with the lead battery manufacturers. The lead oxide has value only as a high purity material. Currently the commercial practice is to send this paste recovered from crushing lead acid batteries to the lead smelters who separately process this mix of red lead, lead sulfate with carbon to obtain a crude lead metal product. This lead metal is then separately reacted with flux and air to remove the contaminating impurities such as antimony, barium, calcium, sulfur, copper, arsenic and other metals.
In U.S. Pat. No. 4,222,769 spent battery paste is desulfurized and then transformed into metallic lead by roasting in the presence of a carbon reducing agent.
U.S. Pat. No. 4,769,110 discloses treating exhausted lead acid battery paste with sodium hydroxide to produce a solution of sodium sulfate and a desulfurized paste which is subjected to electrowinning to produce metallic lead.
International Publication No. WO99/44942 discloses a process of producing lead monoxide from spent lead battery paste using fluxing agents and an organic reducing agent in a calcination step at a temperature of 400° C.-40° C.
U.S. Patent Publication No. 2006/1124094 to Guerriero discloses high purity lead hydroxide and lead oxide from spent acid battery paste that has been desulfurized and converted into a carbonate or hydroxide and then calcinated at 500° C. to obtain pure PbO. The multi-step process includes subsequent treating with acetic acid. The lead acetate solution was treated with an alkali or alkaline earth hydroxide to produce lead hydroxide.
U.S. Patent Publication No. 2010/043600 to Martini discloses a process for recovery of high purity lead compounds from electrode paste slime. The process includes dissolving lead oxide in the paste in suitable acid, reducing any insoluble lead dioxide with hydrogen peroxide, a sulfite or sulfurous anhydride, converting the lead oxide to lead sulfate and then treating the lead sulfate in a solution containing an acetate, calcinating the desulfurized material to get impure lead monoxide followed by leaching of the lead monoxide with acetic acid followed by filtering and then treating further with an alkali hydroxide or alkaline earth hydroxide to obtain soluble acetates to get a precipitate of lead hydrate or lead monoxide.
U.S. Pat. No. 7,507,496 to Smith et al relates to the selective removal of sulfate from battery paste and recovering Pb3O4 which has small amounts of impurities and can be separated from the impurities by dissolution.
According to U.S. Pat. No. 4,222,769, an extracted spent battery paste is desulfurized and then transformed into metallic lead by roasting in the presence of a carbon reducing agent.
In U.S. Pat. No. 4,769,116, a paste is obtained from exhausted lead-acid batteries and treated with sodium hydroxide to produce a solution of sodium sulfate and a desulfurized paste. Pure metallic lead is further recovered from the desulfurized paste by electrowinning.
U.S. Pat. No. 5,211,818 discloses a process wherein the paste sludge resulting from the exhausted batteries is treated with a solution of ammonium sulfate and the metallic lead constituent is recovered by electrowinning.
International Publication No. WO99/44942 discloses a process of producing lead monoxide from spent lead batteries using fluxing agents and an organic reducer in the calcinations step at a temperature of 400° C.-450° C.
Currently a significant amount of the lead oxide paste used in making electrodes for lead acid batteries utilizes a material called leady-lead oxide. Typically this material is made in the Barton process by heating lead metal to 350-500° C. to keep it molten and passing controlled amounts of air or oxygen through it to partially oxidize it to litharge and 25% lead with strong agitation. The lead oxide (litharge) that forms initially contains very fine lead metal which is intimately mixed into the litharge and more slowly reacts. This leady lead oxide which is screened and classified and usually contains about 15-30% lead metal can be used to form lead acid battery electrodes. When this material is introduced into a rake furnace with air at about 500° C. it slowly converts to pure red lead (Pb3O4). In either case the starting material is pure lead metal for the raw material and this must be carefully oxidized.
Alternatively, mixed lead oxides recovered from battery lead oxide pastes are mixed with carbon and smelted directly in a furnace to make molten lead. Then the resulting lead in ingot form is shipped to a plant which has a Barton reactor or ball mill process to be oxidized to the leady lead oxide. The material is subsequently oxidized in another furnace to red lead or pure litharge depending upon temperature and other conditions. This prior art procedure is more costly, requires greater energy expenditure, and requires pollution control.